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The number of CTs per phases will depend on the protection design for that particular circuit breaker, as well as whether busbar protection is required for the board. It will also depend on the company policy for sharing CTs.

The number of CTs per phases will depend on the protection design for that particular circuit breaker, as well as whether busbar protection is required for the board. It will also depend on the company policy for sharing CTs.

Regards,

Alan.

It is possible to share the CT for overcurrent protection and earth fault protection?

As I said, it depends on the protection design and operating company policy. It would also be possible by altering the connections to the relay to achieve the same arrangement using only the three phase CTs and not use a separate one for earth. You need to ensure that you order the correct specification CTs for your protection application. It would be possible (but most companys would think unwise) to use the same CTs for backup overcurrent / earth fault as well as a high speed protection scheme such as unit and / or accelerated distance as well.